Papers by Author: Sheng Qiang Wang

Abstract: Aluminum nitride (AlN) film as a piezoelectric material has been used widely, particularly in vibration energy harvester due to its unique and enhanced properties such as high temperature resistance and compatibility with CMOS processes. In this work, AlN film with (002) preferred orientation was prepared on silicon wafers by pulse DC reactive magnetron sputtering (RMS), and the properties such as peak intensity, full width at half maximum (FWHM) and surface morphology were investigated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The preferred orientation was found to be sensitive to deposition conditions such as gas flow rate, power, bottom electrodes materials and substrates temperature. The results shows that the intensity was 1.1×10⁵ counts, the FWHM was 1.9owhen the temperature was 260°C. The film was used to fabricate the vibrated energy harvester successful and the power density reached about 3000uW/cm³ at the vibration frequency under 1g acceleration.

Abstract: It is presented a fabrication processing of a two step method in deep silicon etching for MEMS applications using an the UK company Surface Technology Systems plc (STS), inductively-coupled plasma (ICP) etch technique STS ICP deep dry etching system. A brief introduction of schematic process of etching deep trenches on silicon substrate is first given, then with two step method for etching deep trenches. The film bulk acoustic resonator (FBAR) devices have been fabricated using STS ICP deep dry etching system with maximum etch rate of 4.6μ m/min, depth more than 450μm and sidewall roughness no more than 0.14μm. At the end of the second step process, the etch selective ratio of silicon to silicon oxygen is enhanced to ensure the device yield. At the same time, the negative effects such as microloads effects, footing effects, lag effects and micrograss effects are suppressed effectively.

Abstract: This work focuses on the development of a biaxial fully differential capacitive microaccelerometer with a single proof-mass. Its design, optimization and fabrication are discussed in detail. Structure and geometric parameters are optimized by multidisciplinary design optimization, enabling ±1g operating range, 1182Hz resonant frequency, 97 fF/g sensitivity, 4.1mg resolution and 0.68 damping ratio. Silicon-on-glass (SOG) bulk micromachining and inductively coupled plasma (ICP) etching technologies are adopted to fabricate this accelerometer.

Abstract: It is known that the wet chemical etching of silicon in alkaline solution has attracted wide attention due to its advantages such as lower cost, simpler setup, higher rate, smoother surface at micro level, higher degree of anisotropy, and lower pollution. In this paper, the key processes of fabricating vacuum microelectronic accelerometer and slits are presented. The cone curvature radius of the silicon tip arrays less than 30nm was fabricated with wet anisotropic etching of silicon in 33wt. % KOH solution at 70°C added potassium iodine (KI) and Iodine (I2) as additive and the cone aspect ratio was about 0.7. Smooth surface after etching in 33wt. %KOH solution added isopropyl alcohol (IPA) at 80°C was obtained and lateral etching was less than 5um after etching several hours for etching depth over 400um. Scalar slits with bottom width 25um and depth 500um were attained. A constant etch rate lead to precise and reproducible production. The test result reveals that the process to a specific occasion can reach practical requirements.

Abstract: This paper presents a simple but reliable fabrication process for microfluidic devices on glass substrate using wet etching technology. Instead of using expensive Pyrex glasses as substrates and depositing expensive metal or polysilicon/amorphous silicon as etch masks in conventional method, glass slide is used as substrate and a single-layer negative photoresist RFJ-220 is used as the etching mask. The etch rates, generation of defects, undercut ratio and surface roughness are studied. In order to achieve high etching depth and smooth surface, buffered oxide etching with hydrochloric acid as additive is proposed. By proper cleaning and long-time hard baking, the undercut ratio can approach to 1. An 110μm depth microchannel with smooth surface is achieved. This fabrication process leads to a considerable reduction of process steps, fabrication time and material consumption. With this technique, we successfully fabricated a microfluidic device, which is used in the capture of hepatoma cells HepG2.